An A-mode ultrasound transducer is tracked in three-dimensions by an optical position tracking system as the transducer is scanned over the skin to generate measurements of bone surface distance from the transducer. A processor correlates the ultrasound data with position and orientation data to generate...http://www.google.de/patents/US6106464?utm_source=gb-gplus-sharePatent US6106464 - Apparatus and method for bone surface-based registration of physical space with tomographic images and for guiding an instrument relative to anatomical sites in the image
